Nanoscale study gives new
insight into heat transfer in biological systems
Troy, N.Y. - One of the first things we learn in
chemistry class is that solids conduct heat better than liquids. But a
new study suggests that in nanoscale materials, this is not
necessarily the case.
Using computer simulations, researchers at
Rensselaer Polytechnic Institute have found that heat may actually
move better across interfaces between liquids than it does between
solids. The findings, which were published online Oct. 11 in the
journal Nano Letters, provide insights that could prove useful in
fields ranging from computer chip manufacturing to cancer treatment.
Conduction is the movement of heat from a warmer substance to a cooler
substance, as when a spoon heats up after sitting in a cup of hot soup.
"Liquids generally have low thermal conductivity when compared to
solids," says Pawel Keblinski, associate professor of materials
science and engineering at Rensselaer and coauthor of the paper. "For
example, diamond is one of the best conductors around, with a
conductivity of about 5,000 times that of water." Metals also tend to
be good conductors, which is why the same spoon would normally feel
cold to the touch -- it conducts heat away from the hand.
But this conventional wisdom refers only to "bulk" thermal
conductivity, which occurs at the macroscale. In nanoscale materials,
the conductivity across interfaces plays a major role. "Conductivity
at the interface of two materials is controlled by the nature of the
interaction between molecules," says Shekhar Garde, associate
professor of chemical and biological engineering at Rensselaer and
also coauthor of the paper. "Even if the two substances are good
conductors, the nature of the interface could affect heat transfer
between them."
Garde and Keblinski performed molecular simulations of a variety of
interfaces and found that thermal conductivity between liquid
interfaces turns out to be surprisingly high.
The findings could have immediate practical application for cancer
therapy, according to Keblinski. "Scientists are developing cancer
treatments based on nanoparticles that attach to specific tissues,
which are then heated to kill the cancerous cells," he says. "It is
vital to understand how heat flows in these systems, because too much
heat applied in the wrong spot can kill healthy cells."
Garde's and Keblinski's research also could be important to the
electronics industry, because of the growing interest in nanocomposite
materials for computer chips, which generate a great deal of heat.
Chip designers are increasingly combining solid surfaces with softer
organic materials, and understanding heat flow will be a key aspect of
continuing to shrink the dimensions of chip components, the
researchers say.
The findings also provide more fundamental insights that are
extremely important for understanding any system with nanoscale
features, which tend to have huge numbers of interfaces, according to
the researchers.
Biological systems are a key example. The surfaces of proteins,
DNA, and other biomolecules interact with water to form the very basis
of life. In water-based solutions, proteins instinctively fold into
unique three-dimensional structures, which do much of the work in the
body. Misfolded proteins also are implicated in diseases such as
Alzheimer's and Parkinson's, and the ability of proteins to function
depends on how much they can vibrate in their folded state.
The next step, according to Keblinski and Garde, is to focus on
studying heat transfer between proteins and water, which will give
them a better understanding of how water governs protein dynamics.
20-October-2005
Source / Further
information:
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Nanotechnology at Rensselaer
In September 2001, the National Science Foundation selected
Rensselaer as one of the six original sites nationwide for a new
Nanoscale Science and Engineering Center (NSEC). As part of the
U.S. National Nanotechnology Initiative, the program is housed
within the Rensselaer Nanotechnology Center and forms a
partnership between Rensselaer, the University of Illinois at
Urbana-Champaign, and Los Alamos National Laboratory. The mission
of Rensselaer's Center for Directed Assembly of Nanostructures is
to integrate research, education, and technology dissemination,
and to serve as a national resource for fundamental knowledge and
applications in directed assembly of nanostructures. The five
other original NSECs are located at Harvard University, Columbia
University, Cornell University, Northwestern University, and Rice
University.
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Rensselaer Polytechnic Institute, founded in 1824, is the
nation's oldest technological university. The university offers
bachelor's, master's, and doctoral degrees in engineering, the
sciences, information technology, architecture, management, and
the humanities and social sciences. Institute programs serve
undergraduates, graduate students, and working professionals
around the world. Rensselaer faculty are known for pre-eminence in
research conducted in a wide range of fields, with particular
emphasis in biotechnology, nanotechnology, information technology,
and the media arts and technology. The Institute is well known for
its success in the transfer of technology from the laboratory to
the marketplace so that new discoveries and inventions benefit
human life, protect the environment, and strengthen economic
development.
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The National Science Foundation provided
funding for the project. Harshit Patel, a graduate student in
materials science and engineering at Rensselaer, also took part in
the research.
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